i never took the practice test on the web site, but heres some intel for you guys.
i took the dat in july 2006 and with out studying got a 18 sci, 19 acav, 20 pat. The next spring i took the kaplan test prep course ($1200), studied my *** off, did all the online content/questions on their website. i even had 2 weeks off from work so id study all day in the library at school. so i took the DAT the next summer just days after all my studying was done(july2007) and for all my work, my scores went to 19sci, 19acav, 23pat. The one major thing i noticed was that the DAT had gotten way harder...maybe i slept bad or something, but i felt perfectly alert. i did feel bewildered after the test because i was not expecting it to get so much harder, and i thought id have better scores.
so for those of you preparing...dont skimp. be solidly prepared.